Revolutionary new technology will allow more couples to benefit from preimplantation genetic diagnosis

Press Release - 01 September 2006

More couples who are at risk of having a child with a serious genetic disorder will be able to select an unaffected embryo thanks to new technology developed at the Centre for Preimplantation Genetic Diagnosis (PGD) at Guy’s and St Thomas’ NHS Foundation Trust.

The technology is called Preimplantation Genetic Haplotyping (PGH) and will also improve reliability of diagnosis and increase the success rate.

The centre has been using PGH for three months and has already achieved five pregnancies using the new technology.

Preimplantation Genetic Diagnosis is a technique used to help couples who are at risk of having a child with a serious genetic disorder, for instance cystic fibrosis, sickle cell disease and spinal muscular atrophy, to select an embryo which will be unaffected.

Although most couples seeking PGD are fertile, they will require IVF treatment like that used for infertile couples. A single cell is then taken from each embryo and analysed to distinguish between the embryos which carry a genetic disorder and those which don’t. One or two unaffected embryos are then transferred to the woman’s womb in the hope that this will result in a pregnancy unaffected by the specific genetic condition.

Due to the complexity of diagnosing genetic disorders in embryos up until now clinicians have only been able to diagnose relatively common conditions and more importantly those where the gene change (mutation) is the same for all those affected.

However PGH will revolutionise what can be offered by diagnosing more conditions, more accurately. PGH involves clinicians firstly amplifying the DNA from the single cell they have extracted from the embryo to replicate the cell’s genetic material by a million times.

DNA finger printing is then used on the cells. This finger printing enables them to distinguish between the chromosomes carrying the affected gene and those that do not. This means that they can track the affected gene without having to look at the actual mutation.

The centre has already started to use the PGH technology for cystic fibrosis so that PGD can be made available to couples other than those carrying the common mutation.

For couples who are at risk of having a child with an X linked disorder (where females carrying the disorder are not affected but the 50% of males who carry it are) like Duchenne and Becker muscular dystrophy PGH will also increase the number of embryos that can be implanted.

Previously PGD could only sex the embryos making sure only unaffected females were used. It was not possible to diagnose affected from unaffected male embryos. The new technology allows clinicians to identify unaffected male embryos as well increasing the total number of embryos available and improving the chance of pregnancy.

Alison Lashwood, Consultant Nurse in Genetics who worked with the team who developed PGH, said: “Preimplantation genetic haplotyping has revolutionised the service we can now offer. It puts together two technologies which have been used before, but it is the combination of these that has made the major difference.

“We are thrilled to have developed this technology as it opens up new possibilities to a number of couples who are at risk of conceiving a child with a serious genetic disorder.

“The development of PGD in the early 1990s was groundbreaking. Since then it has helped many couples in the UK and Eire who were at risk of having a child with a serious genetic disorder. The development of PGH takes PGD to a whole new level allowing us to help even more couples have unaffected babies.”